Frozen section of skeletal muscle stained with nonspecific esterase. (Original magnification:  100x)

A 45-year old male firefighter with diabetes mellitus presents with chief complaint of lower back pain, right proximal thigh weakness, and minimally elevated CPK. Spine imaging shows multi-level degenerative joint disease and moderate spondylolisthesis.  A skeletal muscle biopsy is obtained from the patient’s right thigh.  What findings are seen in the esterase stained frozen section shown of the right rectus femoris?

 

Answer: The findings are those of mild active/ongoing denervation-type change. The muscle fibers of interest are variably atrophic and acutely angulated with a suggestion of a tendency toward small group atrophy.  The frozen section shows the muscle fibers of interest with over-reactivity with the esterase preparation (increased staining intensity, dark), diagnostic of denervation-type change.  Mildly elevated CPK levels may be seen in the setting of denervation-type change.

The case shows denervation-type changes; therefore, it is not normal.  No ragged red fibers are present to suggest mitochondrial myopathy.  No endomysial chronic inflammation is seen for diagnosis of polymyositis-type injury pattern.  No dystrophic changes (increased endomysial fibrosis, fatty replacement, or muscle fiber injury) are seen to support a dystrophic process.

References:

Cai C, Anthony DC, Pytel P. A pattern-based approach to the interpretation of skeletal muscle biopsies. Mod Pathol. 2019 Apr;32(4):462-483. PMID: 30401945.

Dubowitz V, Sewry CA, Oldfors A. Neurogenic Disorders. In: Muscle Biopsy: A Practical Approach, 5th ed. Elsevier, London, United Kingdom; 2021: 201-213.